Many contemporary electronic devices have the facility to connect with an accessory apparatus such as a peripheral audio apparatus. For instance, mobile telephones, tablets, laptop computers and the like are examples of electronic devices that are operable with an accessory apparatus such as a headset, for example, that is external to and distinct from the electronic device. Headsets typically comprise mono or stereo speakers for audio playback and a microphone for voice communication.
Such external accessory apparatus may, in use, be physically connected to the electronic device via a mating connector such as a plug and socket arrangement. For instance, many headsets have a jack plug for connection to a suitable jack socket on the host electronic device. A well-known arrangement for a jack plug and its associated socket is the 3.5 mm TRRS (Tip-Ring-Ring-Sleeve), which has four contacts for left audio, right audio, microphone, and ground return. In one known arrangement, the tip (T) and first ring (R1) are used for left (L) and right (R) audio respectively, for example left and right loudspeakers, with the second ring (R2) and sleeve (S) used for the ground (G) and microphone (M) respectively. It will be appreciated that different arrangements for the left and right audio, microphone, and ground contacts are also possible.
Advantageously the electronic device should be able to automatically detect whether or not an accessory such as a peripheral audio device is connected. Typically therefore the device will include a socket monitoring arrangement associated with the socket to detect whether or not a suitable mating plug is correctly inserted in the socket.
In some instances the socket monitoring arrangement may comprise a mechanical switch which is activated by insertion or removal of a plug from the socket. For instance a mechanical switch could be located at the end of the socket and biased to a first state, e.g. open, if a plug is not fully inserted but which is moved to the other state, e.g. closed, when a plug is fully inserted. Mechanical switches may however be subject to wear and tear in use and may fail over time or the action of the switch may become blocked by dirt etc. accumulating in the socket.
As an alternative in some instances independent first and second socket contacts may be arranged to contact one pole of the plug, usually the tip, when correctly inserted and the electrical properties of the first and second socket contacts monitored. When the plug is fully inserted the first and second socket contacts are effectively shorted together via a low resistance path provided by the tip of the plug. When the plug is removed the first and second socket contacts are open circuit. The electrical properties of the first and second socket contacts may be monitored to detect when the two contacts are electrically connected as an indication of the mating status of the plug. However the distance between the first and second socket contacts is relatively small and moisture within the socket, or some dirt or foreign objects could provide a conductive pathway between the contacts.